Radio phonograph amplifier



May 15, 1934. s. w. SEELEY RADIO PHONOGRAPH AMPLIFIER Filed Oct. 5, 1929Patented May 15, 1934 UNITED STATES PATEN OFFICE RADIO PHONOGRAPHAMPLIFIER Stuart W. Seeley, Jackson,'Mich., assignor, by mesneassignments, to Radio Corporation of America, New York, N. Y., acorporation of Delaware My invention relates to a sound reproducingsystem, and in particular to a system for the electric reproduction ofsound from either radio waves or phonograph records at will.

An object of my invention is to devise an electric reproducing systemfor phonographs in which the audiofrequency stages of a radio receiverare employed for the amplification of the phonograph pick-up currents.

A further object of my invention is to devise a phonograph reproducingsystem in which the phonograph pick-up element is connected in serieswith the input circuit of the detector tube in a radio receiver.

Still another object is to devise an electric reproducing system inwhich the audio stages of a radio receiver are employed for amplifyingthe pick-up current, and in which the pick-up element is connected intothe input circuit of the detector tube by a plug and jack connectionwhich automatically changes the operation of the detector tube from thatof a detector to that of an amplifier. More specifically, my inventionprovides means for connecting -a phonograph pick-up device to the inputcircuit of a detector tube which is normally maintained at a highnegative potential for detector action, and'which upon the insertion ofthe pick-up device into the circuit automatically changes the biasingpotential to cause the detector tube to function as an amplifier.

The single figure of the drawing illustrates my invention as applied toa commercial radio receiver which comprises a tuner compartment A, anamplifying and detecting compartment B, and

' a compartment C containing the audio frequency 1 tubes employed are ofthe uni-potential cathode 'type with heater.

The uni-potential cathodes of the amplifiers are connected to a commonconnection 2 which is grounded to the metallic casing of compartment Bas at (0) through a connection including a fixed resistance R0 incompartment C and the volume control resistance Rcc. The cathode-returnterminals of the input circuits of the amplifiers are connected to acommon connection 3 which is connected to the metallic casing ofcompartment B as indicated at (c). The heaters of the amplifier anddetector tubes are supplied with heating current from secondary winding5 of transformer T5. The midpoint of secondary winding 5 is grounded tothe metallic casing C as indicated at (d). The plate current supplysource for the amplifier and detector tubes includes a full waverectifier tube RT, the filament of which is heated from winding 6, andthe plate elements of which are connected to opposite terminals ofwinding 7. The midpoint of winding 7, which constitutes the negativeterminal of the plate current supply, is grounded to the metallic casingC as indicated at (e) The midpoint of winding 6, which constitutes thepositive terminal of the rectifier, is connected to a filter unitincluding choke coils 8 and 9, resistance 10 and 11, and condensers 12,13 and 14. Choke coils 8 and 9 and resistances 10 are included in seriesin the positive side of the plate supply circuit, while resistance 11and condensers 12, 13 and 14 are connected in shunt to the plate supplycircuit as shown. The plate circuit for the radio frequency amplifiersA1 to A5 is-completed from the positive side of the rectifier filterthrough wire 15 to winding 16 of the loud speaker LS, and throughwinding 16 to a common wire 4, to which the plate circuits of the radiofrequency amplifiers are connected. The plate circuit of the detector Dis completed from positive terminals 17 of the rectifier filter throughprimary winding of transformer T6, through radio frequency choke coilRC, to the plate element of the detector. The cathode of detector D isgrounded to the metallic casing C by a connection including biasingresistance R2 which is connected to the frame of a jack J mounted onmetallic compartment C. A by-pass condenser C3 is connected between theplate and cathode elements of detector D to by-pass the radio frequencycurrent, and a bypass condenser C10 is connected from the detectorcathode to the conductor 3 and to the casing B by connection C. Thecathode-return terminal of the input circuit of detector D is groundedto metallic compartment B and to wire 3 through normally closed jackcontacts 18 and 19. The midpoint of the secondary winding of transformerT6 is grounded to metallic casing C, and the end terminals of thewinding are connected, respectively, to the grids of a push-pullamplifier A6A'7. The cathodes of amplifiers A6 and A7 are heated bycurrent supplied from winding 20 of transformer T5. The midpoint ofwinding 20 is grounded to casing C through a biasing resistance 21. Theplate elements of amplifiers A6 and A7 are connected respectively toopposite terminals of the primary winding of transformer T7, and platecurrent is supplied to these amplifiers by a connection 22 from betweenchoke coils 8 and 9 on the rectifier filter to the midpoint of theprimary winding of transformer T7. The secondary of transformer T7 isconnected to the operating winding 23 of loud speaker LS. A resistanceR3 shunted by a condenser C4 is connected from one terminal ofmagnetizing winding 16 of loud speaker LS to metallic casing C for thepurpose of supplying additional magnetizing current to winding 16 overthat supplied by the plate currents of amplifiers A1 to A5.

24 indicates a plug the leads of which are connected to a phonographpick-up device PC whereby the audiofrequency stages of the radioreceiver may be employed for the electric reproduction of phonographrecords. The sleeve of plug 24 is adapted to make connection with a jackcontact to connect resistance R5 in parallel with resistance R2. The tipof plug 24 makes contact with spring contact 18 of jack J to completethe grid circuit of detector D through the phonograph pick-up device andto open contact between contacts 18 and 19.

Operation of the arrangement is as follows: With the plug 24 removedfrom jack J, contacts 18 and 19 are closed, and the grid-cathode circuitof detector D includes resistance R2. The drop in potential acrossresistance R2, due to the space current flowing through it, maintainsthe grid highly negative with respect to the cathode, so that the tubeoperates on the lower bend of its characteristic curve. This operationis commonly referred to as plate-circuit detection. Incoming radio wavesselected by tuner A are amplified by radio amplifier stages A1 to A5,detected by D, and the resultant audiofrequency currents are amplifiedby the push-pull amplifier A6A7, and reproduced in the loudspeaker LS.The volume of the reproduction is controlled by regulating resistanceRoc, which is included in the input circuits of the radiofrequencyamplifiers and determines the value of the negative bias.

Upon inserting plug 24 into jack J for phonographic reproduction, theinput circuit of detector D is broken at contacts l819 and thephonograph pick-up device PC is connected in series with the gridcircuit by the tip and sleeve of the plug. Resistance R5 isautomatically connected in parallel with biasing resistance R2 upon theinsertion of the plug, and the effective or combined biasing resistancethereby produced is such that the tube D operates as an amplifier on thestraight line portion of its characteristic curve. For example, in onecommercial embodiment of my invention, resistance R2 is of the order of20,000 ohms while resistance R5 is of the order of 1000 ohms. It will beunderstood, however, that the values of these resistances will bedetermined by the characteristic of the detector tube employed.

The currents generated in the pick-up PC are amplified by tube D andagain amplified by the push-pull stage A6A7 before being transmitted tothe loud-speaker LS. The volume of the reproduction may be controlled inany desired manner, preferably by the usual control incorporated in thepick-up device.

While I have described but one commercial embodiment of my invention, itis obvious that certain other arrangements could be substituted withoutdeparting from the spirit of the invention. For instance, a switch maybe substituted for a jack in cases where the phonograph and radioapparatus are incorporated in a single instrument. It is desirable insuch a case to combine the motor control switch or the main phonographcontrolling means with my bias controlling switching means so that asthe turntable is thrown into operation change in biasing resistanceadapting the detector for audio amplifying is accomplished in a singlecontrol. tact 30 on the phonograph jack 24 is connected in a generalmanner at 32. The conductor 33 connects the supply voltage main with theother side of the motor. The other side of the supply line is groundedat 34 so that when the phonograph jack is inserted the phonograph motorswitch is closed simultaneously with the changing of the bias abovereferred to.

What I claim is:

In a radio phonograph combination, a radio receiver including a vacuumtube detector, an audiofrequency amplifier, and a sound reproducer, saidvacuum tube detector being provided with input and output'circuits, anda resistance common to said circuits, a phonograph pick-up device, aturntable, an electric motor for operating said turntable, and meansprovided to control simultaneously the connection of said phonographpick-up, the value of said common resistance and the supply circuit forsaid phonograph motor. 7

STUART WM. SEELEY.

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